Stability and Bifurcation in Reinforced Boreholes
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Rock nailing of a borehole is considered as a means to reinforce the rock and increase its borehole failure strength. The technique is modeled using Cox’s original shear-lag method. In the continuum sense, nail reinforcement is viewed as a body force that acts as a confinement. The finite element formulation of the reinforced elastoplastic borehole is presented and results from an elastic analysis with stiff nails are compared against existing analytical solutions for elastic rocks with rigid nails. The formulation couples the mechanical behavior of the rock with the nail-rock contact law equation that have to be solved in a coupled manner. The bifurcation condition for borehole failure in a Cosserat elastoplastic rock is subsequently extended to a reinforced borehole for stability analysis.
KeywordsBifurcation Condition Borehole Stability Finite Element Method Formulation Strain Increment Vector Elastoplastic Constitutive Relation
This work has been performed as a part of the research project “Formation reinforcement for wellbore stability and sand control” funded by the PETROMAKS programme of the Research Council of Norway and BP Norway (Project number 215667/E30).
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